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Sodium channel in isolated human brain macrophages (microglia)
W Nörenberg1, P Illes, P J Gebicke-Haerter
1Department of Pharmacology, University of Freiburg, Germany.
Abstract:
Human brain macrophages (microglia) have been isolated from mixed brain cell cultures initiated from explants of neurosurgical adult human tissue in one step according to a method developed for rat microglia. Cells were characterized enzyme-histochemically (NDPase) in mixed and immunocytochemically (anti-CD 14) in mixed and isolated cultures. Purified cells were used to investigate in more detail membrane currents by the patch clamp technique. In 14 cells microdialyzed with a standard, K(+)-containing intracellular solution there was no indication for a hyperpolarization-induced K(+)-inward current characteristic for newborn rat microglia. However, in 12 cells depolarizing pulses initiated a rapidly inactivating inward current which was followed by an outward current (in 4 cells). The outward current appeared to be carried by K+, since it was absent in another 18 cells, recorded by micropipettes containing Cs+ instead of K+ as the main intracellular cation. The depolarization-induced inward current persisted under these conditions. This current was inhibited by tetrodotoxin (5 microM) and by substitution of Na+ by choline in the bath solution. It is suggested that this Na(+)-current is specifically expressed in macrophages derived from adult brain.
Insights
Researchers isolated human brain macrophages (microglia) and studied their membrane currents. A sodium (Na+) current, not seen in rat microglia, was identified in adult human microglia.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia are the primary immune cells of the central nervous system.
- Understanding microglia function is crucial for neuroinflammation research.
- Previous methods for isolating microglia were often complex or species-specific.
Purpose of the Study:
- To develop a simplified method for isolating adult human microglia.
- To characterize the membrane currents of isolated adult human microglia.
- To investigate potential differences in ion channel expression between human and rat microglia.
Main Methods:
- Isolation of microglia from adult human brain tissue explants.
- Enzyme-histochemical (NDPase) and immunocytochemical (anti-CD 14) characterization.
- Patch clamp electrophysiology to analyze membrane currents.
Main Results:
- A rapidly inactivating inward current, dependent on sodium (Na+), was observed in response to depolarizing pulses.
- This Na+ current was inhibited by tetrodotoxin and sodium-free solutions.
- A potassium (K+)-dependent outward current was also detected in some cells.
- The characteristic hyperpolarization-induced K+ inward current found in rat microglia was absent.
Conclusions:
- A novel, tetrodotoxin-sensitive Na+ current is specifically expressed in adult human microglia.
- This finding suggests distinct electrophysiological properties of human microglia compared to rodent models.
- The simplified isolation method facilitates further research into human microglia function.